Method of forming a reinforced seamless tubular element



Dec. 17, 1968 A. s. PETZETAKIS METHOD OF FORMING A REINFORCED SEAMLESSTUBULAR ELEMENT Filed Oct. 24. 1966 4 Sheets-Sheet z FIG. 5

FIG.4

INVENTOR Aristovoulos G. Petzetakis I/W, 94AM 1968 AG. PETZETAKIS3,416,982

METHOD OF FORMING A REINFORCED SEAMLESS TUBULAR ELEMENT Filed Oct. 24,1966 4 Sheets-Sheet 5 E i 3 \Z 9 6a j/g v I N VEN TOR flfi/s 7'0 v0 0/.as G". P: 72 5779/05 7" ENE YS Dec. 17, 1968 A. G. PETZETAKIS METHOD OFFORMING A REINFORCED SEAMLESS TUBULAR ELEMENT Filed Oct. 24, 1966 4Sheets-Sheet 4 Ill-Illnlnllllllll-Illllll ll'l'l'llllllll.

llllllllllllllllll United States Patent 14 Claims. '01. 156-193)ABSTRACT OF THE DISCLOSURE A method of forming integrally reinforcedarticles by continuously extruding a relatively high strengthreinforcing core material coaxialiy within a continuously extrudedstream of a softer matrix material and continuously extruding thecoaxially disposed core and matrix materials to effect an intimate bondtherebetween andv provide a continuous integrally reinforced strip. Atubular element is then formed by winding the integrally reinforcedstrip upon itself in a helix and bonding the successive loopsof thehelix to one another. If desired, intermediate materials can beinterposed between the core and matrix materials and coaxially extrudedtherewith.

The application is a continuation-in-part of my copending applicationsSer. No. 220,291 filed Aug. 29, 1962, issued as US. Patent No. 3,290,727and Ser. No.'337,692 filed Dec. 18, 1963, issued as US. Patent No.3,299,908, which were based upon Greek patent application Ser. No.24,307 filed Sept. 5, 196 l.

The present invention relates generally to a method for the manufactureof rigid-flexible articles and more particularly to a method forproducing integrally reinforced seamless rigid or flexible tubing,adapted to withstand an internal pressure or vacuum, as well as otherintegrally reinforced rigid-flexible composite articles such as conveyorbelts, strips or the like. As the description herein progresses it willbe apparent that any readily extrudable supply material such assynthetic resin and the like, can be employed in the method of thepresent invention. As used herein the term synthetic resin material"embraces the use of any thermoplastic or thermosetting materials ormixtures thereof. in addition, the present invention contemplates withinits scope the utilization of natural and synthetic rubbers and theirmixtures with synthetic resins.

More especially, the present invention comprises a method for themanufacture of a tubular element comprising two plastic or readilyextrudable materials compatible with each other wherein helicalreinforcement is included in a matrix of softer material, and whichtubular element can comprise not only a finished end product in and ofitself but also an intermediate product or workpiece which is readilysusceptible to further or subsequent working to produce other articlesof commerce. While as aforementioned any plastic or readily extrudablema terials which are compatible with one another can be utilized inpracticing the present invention, thermoplastic materials are preferablyemployed. One embodiment of the present invention disclosed hereingenerally comprises the steps of continuously forming a composite stripcomprising a relatively strong reinforcing core material embedded in andfused or bonded to a relatively soft matrix material and continuouslyfabricating therefrom a tubular structure in which said core materialprovides an integral helical or spiral reinforcement of the tubular wallformed by said matrix material.

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Accordingly, it is a principal object of the present invention toprovide a novel method for forming seamless tubing having integralreinforcement to provide maximum mechanical strength by effecting asubstantially perfect bond between the matrix and reinforcement of thetubing.

It is a further objective of the invention to provide for themanufacture of reinforced seamless tubing having any desired flexibilityor rigidity with optimum resistance to radial pressures withoutimpairing the axial strength thereof and without impeding the flow ofmatter through said tubing and wherein the reinforcing material replacesan equal quantity of the softer material in the wall of the tubing, sothat the total quantity of material used for the production of thereinforced tubing does not exceed that which would be required for theproduction of a non-reinforced tubing. This objective is obtained bycreating maximum bursting resistance with minimum material.

, It is a further objective of the invention to provide a novel methodfor the manufacture of rigid-flexible articles and more particularly ofarticles integrally reinforced with a reinforcement having a determinedcross-section whereby two materials compatible with each other but ofdifferent plasticity are simultaneously extruded through a fixed head,the harder material being extruded within the stream matrix of thesofter material at a determined crosssection at the initial phase of theprocess, while at the subsequent phases of the process during which thefashion for the formation of the finished end product is performed. onlythe soft matrix is fashioned and the harder material maintains itsinitial cross-section owing to the said difference of plasticity of thetwo materials.

it is a further objective of the invention to provide a novel means forthe economic bonding of thermoplastic materials of differing hardnessand other physical characteristics and to distribute them in the properway for building the wall ofa reinforced tubing.

Other objects and the entire scope of the present invention will becomeapparent from the following detailed description and by reference to theaccompanying drawings. It should be understood, however, that thedetailed description and specific examples, while indicating preferedembodiments of the invention, are given by way of illustration only,since various changes and modifications within the spirit and scope ofthe invention will become apparent as the description herein progresses.Reference is now being made to the accompanying drawings which form apart hereof, wherein:

FIGURE 1 is a vertical sectional view of an apparatus employing themethod of the present invention;

FIGURES 2, 3, 4, and S are sections of various tubular elementsmanufactured according to the present invention utilizing the apparatusshown in FIGURE 1;

FIGURE 6 is a vertical section of an apparatus employing a modified formof the present invention;

FIGURE 7 is a fragmentary plan view of a section of belting manufacturedaccording to the present invention; and

FIGURE 8 is a longitudinal sectional view taken gener ally along theline 8-8 of FIGURE 7.

Broadly, the invention comprises initially uniting plastic materials ofdifferent hardness characteristics in a common channel in which aplastic core comprising the harder material is embedded, either with orwithout an intermediate material, in s more ductile, softer matrix toform a supply of efiiuent of uniform width in the form of a strip, witha reinforced or wick-like center which is deposited upon itself. Therespective plastic materials forming the matrix and the core aresimultaneously extruded through a fixed head concentrically of eachother under great extrusion pressure and consequent heat and thereuponconducted to a bonding station. In the process, the combined matrix andits core are intimately and inseparably bonded, and thereafter rotatedin a path of deviation from the initial direction of flow (centralline), through a rotating head which is in substantially continuouscontact with the fixed channel through which the respective matrix andreinforcing core has passed and were joined. The effect of this rotationis to form a substantially circular track for lapped deposition of thecombined materials by ejection of the same from a nozzle through dies,wherein by compression of the ejected and combined matrix and its core,helices are formed between contiguous sides of the matrix and whereby,because of the malleability or soft plastic condition of the softermatrix an endless reinforced integral tubular element is created. It isinherent in the aforementioned process that the softer plastic materialforming the matrix is in a molten condition relative to the harder corewithin the matrix comprising the spiral reinforcement. In fact, thebonded materials are forced under continuous pressure through dies in awinding fashion. This combined windingextrusion through a guide causesthe formation of a flowing strip, which winds, continuously upon itself.The spirals of the winding deposit, retaining the heat of pres sure,remain soft; they overlap and fuse together forming thereby a continuousseamless wall in which is embedded the spiral or helical reinforcement.The tubing thus formed is of circular cross-section, having a continuousspiral core throughout its length, the latter providing controlledreinforcement.

In other words, according to the present invention, a hollow tube ofsynthetic resin material is made by continuously extruding a core of afirst material having a comparatively high mechanical strength,simultaneously extruding a second material which is comparatively softand plastic around the first material, subjecting the materials tosufficient pressure to form a firm bond between them, pushing thematerials through a rotating nozzle. and winding the emerging materialon itself in a guide so that the softer material fuses to form acontinuous hollow tube incorporating a spiral core of the strongermaterial.

it should be apparent that in utilizing apparatus employing the presentinvention the two materials, which are of different hardness andplasticity, are strongly bonded'or fused together in the initial phaseof the process under high pressure and temperature, while at the lastphase of the process only the sealing of the homogeneous and softcovering or matrix material is involved, which is easily achieved byrelatively insignificant pressure.

The covering of the hard core with the softer material in the initialphase of the process aims also at facilitating the passage of the hardercore through the narrow chan nels, since the softer material isinterposed between the hard core and the metallic inner surfaces of thechannels and acts as a lubricant conveying with it the hard core. Thismakes it possible for the strengthening spiral core to be made of veryhard materials which are normally very difficult to extrude. Also, byelongating the narrow channel in the rotating head and by adjusting thecorresponding displacement of the nozzle to various distances from itsaxis of rotation, tubes of different and very large diameters can beobtained. Similarly, as will be described in greater detail hereinafter,additional materials can, if desired, be coextruded intermediate thematrix and reinforcing core.

A particular advantage of the present invention resides in the provisionfor a regular and continuous how of the extruded mass through theextrusion head. This is achieved by means of the passage of the combinedmatrix and core through a fairly narrow "lubricated" channet up to thedie. In the art, extrusion methods heretofore employed result in anirregular flow of the mass into the head which in turn results in thepresence of joining lines along the formed tubular element, caused bysupports such as spiders and the like. This latter mentioned difficultyof the prior art is an especially significant detriment to themanufacture of tubes of large diameter. The present invention whichovercomes such typical drawbacks of the prior art, will be seen toparticularly and readily lend itself to the fabrication of tubes ofunusually great diameters.

In practice, the two materials, after having been bonded in the form ofa strip or cord, move together at the same linear speed through a commonchannel. It will be apparent, however, that should the rate of turn ofeither the extruder screw or the feeding of the respective channels bevaried, the quantitative relation of the one material to the other wouldbe affected. Since both materials, when joined, pass simultaneouslythrough a channel of given diameter, the diameter of the rigid spiralwould thus increase or decrease according to the rate of production ofthe rigid material in relation to the rate of production of the softermaterial comprising the matrix. This is inherent in the process. Thediameter, therefore, of the reinforcing material is directlyproportionate to its rate of production as related to that of the softermaterial. In practice also, the rotational speed of the extrusion head,while variable, should be such that the circumferential velocity of theextrusion nozzle which is adjacent to the die or guide is substantiallyequal to the linear velocity of the strip of the combined material whichis extruded through the nozzle.

Owing to the fact that the axes of both channels in the fixed and therotating heads at their joining point or juncture coincide with the axisof rotation, it is evident that the material, in the form of the saidcord, when entering the channel of the rotating head, will, in additionto its linear movement, also suffer a twisting action around its ownaxis at the rate of one turn for every complete revolution of therotating head. When the materials are in a plastic condition, suchtwisting action has no significance. However, it is obvious that inorder to obtain a tube with a uniform wall, it is necessary that at thisjoining point of the two heads the materials are disposed concentricallyof each other and are of circular cross-section.

The thickness of the spiral core, its pitch, as well as the thickness ofthe wall of the tube can be varied according to the specificrequirements of the type of tube desired to be obtained and also to theproperties of the materials used. According to the elasticity of thesofter material, tubes of different and very high flexibility can beobtained in which the embedded spiral core of the hard material makesthe tube equally strong to withstand high internal pressure or vacuums.

The present method of forming tubular elements, by which the strong coreis firmly bonded approximately in the center of the softer wall,provides a tube of great strength using only a relatively small quantityof materials.

While the reinforcing spiral core increases the resistanceof the tube inits circumferential direction to radial pressures (where the greatestforces act), it does not deleteriously affect (owing to the aforesaidperfect bonding of the two materials) its resistance in its longitudinaldirection, i.e., its axial strength. Moreover, since the spiral coreforms an integral part of the wall of the tube, it is obvious that bythe method of the present invention the tube is reinforced without usingmore volume of material than that which would be required for theproduction of a similar (same size) but non-reinforced tube.

In addition, it will be apparent to those skilled in the art that atubular element after being manufactured according to the presentinvention, can be further processed, as for instance by coatingexternally or internally lining the tube with other protectivematerials. or by further forming the same into other articles such asstrips, belting or the like.

The fact that the passage of the materials from the fixed head into therotating head is effected through channels of small circularcross-section eliminates the problems of lightness and friction at thecontact of the two heads, although the materials passing through thissection are subjected to high pressure. As a result of the foregoing asimple and sturdy construction of the apparatus carrying out thisprocess is possible.

Referring now to FIGURE 1 of the drawings, it will be seen that theapparatus 100 illustrated therein is designed for the simultaneousextrusion of two separate thermoplastic materials. A fixed head 160 hastwo inlets 182 and 180; Inlet 182 communicates through the conduit meansor channel 170 and its extension 172 in the dowel 164, with the circularsection orifice 176 which is in material ejecting communication with thecenter of a first common channel 174.

Similarly, the inlet 180 communicates through the conduit means orchannel 170' with the common channel 174 which is situated in a secondfixed member 110. Inside the fixed member 110 is a rotatable member 140driven by a cooperating toothed wheel 154 which is connected through ashaft 156 to a variable speed motor (not shown). The member 140 isrotatable about the axis CL which, in the embodiment of the inventionillustrated, is the center line of the apparatus. This rotatable member140 rotationally engages the bearings 124, 116, and 136.

The rotatable member 140 has a conduit means or channel 148 whichconnects with the channel 174 of the fixed member, so that at theirconnection point 122 the axis of each channel coincides with the axis ofrotation. The two channels must both be of circular cross-section attheir connection so that they will be in continuous communication whilethe one rotates.

Channel 148 leads to, and is in communication with, a nozzle 150integral with the rotating member 140, which nozzle 150 is displaced adistance r from the axis of rotation CL, so that as member 140 isrotated the nozzle 150 describes a circular track of radius r around theaxis. Corresponding to this circular track is a gap 120 formed betweencircular dies 118 and 132. The external die 118 is fixed to the member110, while the internal die 132 is supported by the shaft 142 of therotating member upon the bearing 134.

In operation of the apparatus utilizing the present invention, amechanically strong material such as rigid PVC (polyvinyl chloride) isforced through inlet 182 and orifice 176 under continuous pressure fromthe extruder, into the center of a stream of softer material, such assoft plasticized PVC which, having been forced through the inlet 180 andchannel 170'. moves along the channel 174.

The temperature of the rigid PVC passing through the extrusion head 160and issuing from the orifice 176 is about 190-200 C. while thetemperature of the softer, plasticized PVC passing through the head 160and issuing around the orifice 176 is about 160-180 C. Therefore, uponthe intimate contact of the two materials in the channel 174, atemperature equalizing heat exchange will take place resulting in alowering of the temperature of the rigid PVC and raising of thetemperature of the pin;- ticized PVC and a consequent increase in thedifference in plasticity between the two materials during theircoextrusion. The thus co-axially disposed materials are pushed togetherthrough the channel 174 and as they are forced to pass through narrowchannels they are subjected to high pressure and are firmly fused orbonded together to form a hard core which is inseparable, when cooled,from the surrounding matrix layer of softer, more plastic material.

The materials so bonded are forced, under the continuour pressureexerted from the extrudcrs, to pass from the channel 174 of the fixedhead to the channel 148 of the rotating head and through the channel 148where they are led to the nozzle 150 from which they are elected intothe gap 120 between the dies 118 and 132 while the nozzle is at the sametime rotating.

The correlation between the rotational speed of the nozzle and theextrusion speed of the materials through it is such that the nozzle,during its rotation, deposits continuously on its circular traclt astrip of material which is wound on itself in a helix or spiral, so thatthe successive loops of the still hot, plastic, surrounding or matrixportion of the strip which is formed of the softer material fuse to forma continuous wall without a scam, thus giving a circular section hollowtube 200 whose wall 210 incorporates an integral strengthening spiralcore 216 and which tube is pushed forward by the succeeding materialejected continuously from the nozzle.

It will be obvious that by extruding the hard material through the smallorifice at 176, an improvement in its physical properties is obtained. Amodification of this method will occur to those skilled in the art,whereby a stretching of the comparatively rigid spiral reinforcingmaterial may be effected when using materials that are susceptible toorientation. If the section of the channel through which the combinedmaterials pass is reduced in cross-section as at 148, one diminishes thediameter of the core whereupon by accelerating the speed of the passageof the core through the channel an automatic stretching of the corewithin the matrix occurs ensuring a relative orientation assuming, ofcourse, the appropriate temperatures are maintained.

A tube of maximum strength is manufactured according to the presentinvention in a continuous and substan tially automatic process using thesmallest possible quantity of materials. Due to the bond between therespective matrix and core, it is quite unnecessary for a greatthickness of the soft material to surround the core. As previouslyindicated, the diameter of the reinforcing spiral is directlyproportionate to the rate of production of the hard material as relatedto that of the softer material. In this connection, attention isdirected to FIGS. 2, 3, 4, and 5, which illustrate samples of tubeswhich can be produced utilizing-the method of the present invention andutilizing the apparatus illustrated in FIGURE 1 including the same dies.

FIGURE 2 particularly illustrates a tube integrally reinforced with aspiral of small diameter.

By increasing the rate of extrusion of the hard material and bydecreasing at the same time the rate of extrusion of the soft material,the diameter of the reinforcing spiral increases as shown in FIGURE 3 inwhich the diameter of the spiral has attained its maximum, being thethickness of the wall of the tube. 1

FIGURE 4 illustrates a tube with a reinforcing spiral of mediumdiameter.

Finally, the tube inFIGURE 5 is derived from that illustrated in FIGURE4, when the tube extruded from the apparatus as in FIGURE 4 is stretchedby a continu ous take-off at a high speed before it solidifiesby'cooling, whereby the tube being stretched becomes thinner at thepoints 210 of the soft material.

Referring now to FIGURE 6 of the drawings, there is shown a modificationof the present invention wherein an apparatus 300 is utilized for thesimultaneous extrusion of three separate plastic materials comprisingspecifically a matrix material 310, a core material 316, and anintermediate material 312. To this end the apparatus 300 differs fromthe apparatus heretofore described by reference to FIGURE 1 in that inaddition to the inlets 380 and 382 for the matrix material 310 and corematerial 316, respectively, the fixed head assembly 360 includes a thirdinlet 384 for the intermediate material 312 which is to be continuouslyinterposed between the matrix and core materials. As with apparatus100,- each of the inlets 380, 382, and 384 are operatively connected tosuitable extruders (not shown) so as to receive a continuous sup ply oftheir respective plastic materials therefrom.

The inlet 382, for the core material 316, communicates through theconduit means or channel 370 and its reduced extension 372 in the dowel364 with the circular section extrusion orifice 376 which is in materialejecting communication with the center of a first common conduit meansor channel 378. Similarly, the inlet 384, for the intermediate material312, communicates through the conduit means or channel 370" and itsreduced extension 373 with the first common channel 378 so as toconvergingly discharge the intermediate material 312 about the strip ofcore material 316 issuing from the extrusion orifice 376. The firstcommon channel 378 will be seen to extend through the fixed headassembly 360 and terminate in a circular section extrusion orifice 376'which is in material ejecting communication with the center of theconverging mouth 375 of a second common conduit means or channel 374which is situated in a second fixed member 311. The inlet 380, for thematrix material 310, communicates through the conduit means or channel370' with the converging mouth 375 of the second common channel 374 sothat the matrix material 310 will be convergingly discharged about thecomposite strip comprising the core material 316 and intermediatematerial 312 issuing from the extrusion orifice 376'.

As in the construction of the corresponding portion of the apparatus100, the second fixed member 311 of the apparatus 300 has disposedthercwithin a rotatable member 340 which is in rotational engagementwith the hearing 317, 324, and 336. The rotatable member 340 isrotatably driven about the axis CL which, as in the previous embodiment,is the center line of the apparatus 300, by means of a suitable toothedwheel or gear 355 carried by the rotatable member 340 which is drivinglyinterengaged with a cooperating toothed wheel or gear 354 connected bymeans of a rotatable shaft 356 to a suitable variable speed motor (notshown).

The rotatable member 340 includes a third common conduit means orchannel 348 which is in fluid communication at its inlet end 349 withthe outlet end 377 of the second common channel 374 at the juncture orconnection point 322 of the fixed member 311 and the rotatable member340. As in the previous embodiment, the channels 348 and 374 will be incontinuous fluid communication throughout the rotation of the rotatablemember 340 since at their juncture 322, the longitudinal axes of theinlet end 349 of the channel 348, and the outlet end 377 of the channel374 coincide with the axis of rotation CL and the cross section of eachchannel is circular.

The channel 348 leads to, and is in fluid communication with, adischarge nozzle 350 integral with the rotating member 340 and havingits discharge orifice 351 displaced radially a distance r from the axisof rotation CL, so that as the member 340 rotates the discharge orifice351 of the nozzle 350 describes a circular track of radius r about theaxis CL. As in the previous embodiment of the invention, the circulardies 318 and 332 define a circular slot or gap 320 which corresponds tothe circular track of the discharge orifice 351 and isin continuousmaterial receiving communication therewith. The external die 318 iscarried by the depending skirt portion of the fixed member 311, whilethe internal die 332 is supported by the shaft 342 of the rotatingmember upon the bearing 334.

This modification of the present invention wherein three separateplastic materials are simultaneounly coaxially extruded is of particularutility when the materials selected for the matrix and core will notsatisfactorily bond directly to one another or are otherwiseincompatible when in direct contact. Thus, according to the presentinvention such incompatibility between particular matrix and corematerials can be readily and effectively overcome by means of anintermedite material which is compatible with, and will intimately bonddirectly to, both the matrix and core materials. For example, rigid PVCand natural rubber. incompatible materials which cannot normally beeffectively bonded directly to one another, can be utilized for the coreand matrix, respectively, when according to the present invention anintermediate material, such as butadlene acrylonitrile rubber which iscompatible with, and will intimately bond directly to, both rigid PVCand natural rubber, is employed as an intermediate bonding layer. Thus,utilizing the apparatus 300, mechanically strong rigid PVC, corematerial 316 is forced through the inlet 382, its reduced extension 372and the orifice 376 under continuous pressure from an extruder (notshown), into the center of a stream of nitrile rubber intermediatematerial 312 which, under continuous pressure from its extruder (notshown) having been forced through the inlet 384, the channel 370" andits reduced extension 373, moves along the first common channel 378. Thethus coaxially disposed materials 316 and 312 are forced firmly andintimately into bonding contact as they are pushed together into andthrough the first common channel 378 and issue as a composite strip fromthe extrusion orifice 376 into the center of a stream of natural rubbermatrix material 310. The natural rubber matrix material 310 which, undercontinuous pressure from its extruder (not shown) has been forcedthrough the inlet 380 and the channel 370', moves into the convergingmouth 375 and along the second common channel 374. The thus coaxiallydisposed PVC core material 316 and the natural rubber matrix material310 are forced firmly and intimately into bonding contact with theintermediate layer of nitrile rubber 312 as the three coaxially disposedmaterials are pushed together into and through ,the second commonchannel 374 where because of the high pressure and temperature they arefirmly fused or bonded together to form an integral composite striphaving a hard mechanically strong core and a soft more palstic matrixwhich are inseparable when cooled from the intermediate bonding layer.The temperatures which should be attained and maintained during theextrusion and bonding, of course, depend upon the particular materialsemployed in the process; however, they are the generally well-knownstandard extrusion temperatures for the particular materials. Inaddition, as

will be apparent to those skilled in the art, if necessary heat, inaddition to that generated by the passage of the materials through thenarrow extrusion channels of the apparatus, can be supplied to thematerials by suitable heating means (not shown) such as electric coilsor the like operatively arranged with respect to the apparatus.

The composite strip, comprising the coaxially disposed rigid PVC core316, the nitrile rubber intermediate material 312 and the natural rubbermatrix material 310, intimately bonded one to the other asaforementioned, is forced under the continuous pressure exerted from theextruders, to pass from the second common channel 374 in the fixedmember 311 into the third common channel 348 of the rotating head 340where it is led to the nozzle 350 from which it is continuously ejectedthrough the consequently continuously rotating orifice 351 into thecircular gap 320 between the dies 318 and 332.

As in the previously described embodiment of the invention, thecorrelation between the rotational speed of the nozzle 350 and theextrusion speed of the coaxially disposed bonded materials therethrough,is such that the nozzle, during its rotation, continuously deposits onits circular track, a strip of composite material which is wound uponitself in a continuous helix or spiral. Thus, the successive loops ofthe still hot, plastic matrix portion 310 of the strip which, in thepresent example, comprises natural rubber, fuse to one another to form acontinuous wall without a seam and thus continuously produce a hollowtubular element 400 of circular crosssection whose wall incorporates astrengthening spiral core 316 continuously intimately and inseparablybonded to the natural rubber matrix 310 by means of the continuousintermediate layer or sheath 312 of nitrile rubber material. Of course,when the desired length of tubing has been formed, it may be severedfrom the tubular element issuing from the circular gap 320.

Referring now to FIGURES 7 and 8 of the drawings, there is shown asection of a length of an integrally reinforced fiat belt 500 producedaccording to the present invention. The belt 500 comprises a relativelysoft plastic matrix material 510, for example plasticized PVC, in whichthere is embedded and intimately bonded a plurality of laterallyextending, longitudinally spaced reinforcing elements 516, formed of astrong rigid material. such as rigid PVC. The fiat belt 500 can bereadily formed by slitting or cutting an integrally reinforced tubularele ment, such as the tubular element 200, FIGURE 1, longi tudinally,subsequent to its issuance from the circular gap 120 between the dies118 and 132. After slitting, which can, of course, be accomplishedcontinuously as the tube issues from the apparatus 100, the resultingweb, formed by the longitudinally slit tubular wall, is flattened whileplastically permanently deformable. by suitable means such as by beingspread over a fiat plane surface or passed over suitable rolls, and canthereafter be wound into suitable rolls or upon take-up reels forconvenient storage prior to further processing. As will be apparent tothose skilled in the art, when the matrix and integral reinforcing coreof the tubular workpiece'element comprise thermoplastic, as opposed tothcrmosetting materials, the development thereof into a fiat belt orstrip by slitting and flattening can be readily accomplished anyconvenient time after the materials have cooled sufficiently to assume apermanenit set by merely heating the composite web during fiatten ng.

Such a fiatdevelopment of an integrally spirally reinforced tube as thebelt 500 will, byvirtue of the integral rigid, laterally extending,longitudinally spaced, reinforcing elements 516, exhibit considerablerigidity about its longitudinal axis but will be sufficiently flexibleabout transverse axes, i.e. longitudinally flexible, that it can bereadily led or wound about pulleys or rollers. The integrally reinforcedbelt 500 thus, as will be readily appreciated, finds particular utilityas a conveyor belt.

While integrally reinforced tubular elements and fiat strips or beltshave been particularly shown and described, it will be apparent thatother rigid-flexible products can be readily manufactured according tothe method of the present invention.

It will thus be seen that the objects of this invention have been fullyand effectively accomplished. It will be realized, however, that theforegoing specific embodiments have been shown and described only forthe purpose of illustrating the principles of this invention and aresubject to extensive change without departure from such principles.Therefore, it will be understood that this inven tion includes allmodifications encompassed within the spirit and scope of the followingclaims.

What is claimed is:

l. A method of forming an integrally reinforced seamless tubular elementcomprising the steps of continuously extruding a strip of a firstmaterial which is comparatively soft and plastic; simultaneouslycontinuously extruding a second material having a comparatively highmechanical strength and injecting the said second material into thecenter of the strip of the first material as a core; continuouslyextruding the thus disposed first and secondmeterials to form by heatand pressure a firm intimate bond therebetween and thereby provide anaxially advancing integrally reinforced composite strip; moving saidcomposite strip laterally in a closed path corresponding to thecrosssectlonal configuration of the tubular element to be formed whilesimultaneously continuing the axial advance of said composite strip;guiding said composite strip so that it winds upon itself in a helix:and bonding the successive loops of said helix to one another to therebyform a tubular element having a seamless tubular wall formed of thefirst material and an integral reinforcing spiral of the second materialintimately bonded thereto.

2. The method defined in claim 1 wherein the second material is injectedinto the center of the strip of the first material through an extrusionorifice.

3. The method defined in claim 1 which includes the steps of slittingthe tubular wall of the tubular element longitudinally and flatteningthe web formed by the longitudinally slit tubular wall to thereby form afiat belt-like strip.

4. The method defined in claim 1 wherein the first and second materialscomprise synthetic resin materials.

5. The method defined in claim 4 wherein the first material comprisessoft plasticized polyvinyl chloride and the second material comprisesrigid polyvinyl chloride.

6. The method defined in claim 1 wherein the first and second materialsare heated during bonding.

7. The method defined in claim 1 wherein a third material is interposedcoaxially between the first and second materials.

8. The method defined in claim 1 wherein the closed path in which thecomposite strip is moved is of circular configuration.

9. The method defined in claim 1 wherein the second material is extrudedinto a core of circular cross-section.

10. A method of forming a reinforced hollow tubular element comprisingthe steps of: continuously extruding a strip of soft plastic matrixmaterial; continuously extruding a core material having a comparativelyhigh strength and simultaneously continuously extruding an intermediatematerial around said core material; continuously injecting said corematerial with said intermediate material disposed therearound into thecenter of said strip of matrix material; continuously extruding the thusdisposed matrix, intermediate and core material to firmly, intimatelyand continuously bond said intermediate material to saidcore and matrixmaterials and thereby provide an axially advancing integrally reinforcedcomposite strip; moving said composite strip laterally in a closed pathcorresponding to the cross-sectional configuration of the tubularelement to be formed while simultaneously continuing the axial advanceof said composite strip; and guiding said composite strip so that itwinds upon itself in a helix wherein the soft plastic material of theadjacent loops of said helix bond to one another to form a continuoushollow tubular element having a strong integral spiral reinforcing coreelement embedded in the wall thereof.

11. The method defined in claim 10 wherein the core material comprisesrigid polyvinyl chloride, the intermediate material comprises butadieneacrylonitrile rubber and the matrix material comprises natural rubber.

12. The method defined in claim 10 wherein the closed path in which thecomposite strip is moved is of circular configuration.

13. The method defined in claim 10 wherein the core material is extrudedinto a core of circular cross-section.

14. The method defined in claim 10 which includes the steps ofcontinuously slitting the tubular wall of the tubular elementlongitudinally and flattening the web formed by the longitudinally slittubular wall to thereby form a flat belt-like strip.

References Cited UNITED STATES PATENTS 2,748,805 6/1956 Winstead 156-1953,013,921 12/ i961 Jacobson 156-191 3,227,596 1/1966 Knowles 161-1442,501,690 3/1950 Prendergast 264-l73 2,632,205 3/ I953 Fitz l-iarris264-173 MORRIS SUSSMAN, Primary Examiner.

US. Cl. X.R.

